There are various options if you would like to have an undetectable hidden room. You can convert a part of your house into the invisible portion. This can be accomplished easily if you choose a windowless room with just one door. By transforming the door into a bookshelf, you can easily camouflage the room behind it. This is the most common approach to having an undetectable hidden room. However, with the passage of time, people have come up with newer ideas and there are many other options you can consider.